Photoelectric tube



PHOTOELECTRIC TUBE Filed Sept. 24, 1937 FIG 4 ATTORNEY Patented Apr. 30, 1940 mete PHOTOELECTRIC TUBE Walter J. Albersheim, New York, N. Y., assignor to Electrical Research Products, 1110., New York, N. Y., a corporation of Delaware Application September 24, 1937, Serial No. 165,453

8 Claims. (01. 250-166) This invention relates to photoelectric tubes and more particularly. to the electrode structure of such tubes.

An object of the invention is to provide an improved form of double anode photoelectric tube.

In an example of practice illustrative of this invention, a cathode plate formed into two hollow quarter-cylinders of quarter-circular crosssection joined along one edge and curved. away from each other so that no portion of either concave surface faces the other concave surface and 9 two anodes are supported from a stem within an evacuated container. tioned respectively in front of a concave surface and parallel thereto. The concave surfaces are sensitized by oxidation and treatment with caesium vapor.

In the preferred method of sensitizing these concave surfaces an electric discharge in oxygen 20 is produced by means of a voltage impressed on the cathode plate and the anodes in parallel.

The uniformly curved quarter-cylindrical shape of the cathode plate facilitates the production of a uniform layer of silver oxide is formed which when treated with caesium vapor under suitable temperature conditions results in a highly eflicient photoemissive surface. 30 Photoelectric tubes according tothisinvention are particularly useful in the projection of sound from theso-called push-pull sound records. When used for this purpose, the anodes are connected 3 separately to the sound circuit. If it is desired anodes may be connectedtogether. The light beam can then be projected on the whole cathode surface without loss of efficiency because there is no separation between the two; concave surfaces 40 of the cathode.

This invention will now be described more in detail having reference to the accompanying drawing.

Fig. 1 shows the structure of a completed photoelectric tube according to this. invention.

Fig. 2 is a cross-section of the tube of Fig. l

perpendicular to the axes of theelectrodes and looking away from the stem.

Fig. 3 illustrates a pumping station suitablefor 50 processing four tubes concurrently.

Fig. 4 is' a schematic electric circuit used in processing such tubes.

Like reference characters are used to designate identical elements in the various figures. The photoelectric tube illustratedinFig. 1 com- Hand ii.

The anodes are posia uniform layer of oxide over the concave surfaces. e Since these surfaces are preferably silver surfaces, J

to project sound fromordinary sound records,th e

prises a glass bulb 5 having a reentrant stem t sealed therein. The stem 5 is provided with a press 1 in which are sealed support wires 8, 9, iii, To the upper ends of wires 8 and It a. mica disc i3 is secured, the wires passing through eyelets in the disc and. being welded thereto. A bent support wire M is welded intermediate its ends to wire 9. One end of wire I l helps to support disc i3, being welded to an eyelet in the disc through which wire i i passes. Cathode 55 con- 1 sists of a sheet of silver formed into two quartercircular cylinders l6 and i! joined along one edge l8. and having support wings l9 and 28. These wings i9 and Marc bent partially around support Wires 8 and iii,respectively, and welded thereto 1 by clips. Anode wires 2i and 22 are welded at one end to support wires II and i2, respectively, and are held in place at their other ends by passing. through holes in mica disc it. These anode wires 2! and 22 are positioned in front of and parallel to the concave surfaces of quarter-cylinders iii and II, respectively, of cathode 35 approximately in a plane passing through the edges of each surface intermediate the two edges and somewhat closer to the outside edge. These wires 2i and 22 are of molybdenum app oximately 10 mils in diameter. A nickel shield 24 is supported from the other end of bent wire i4. To this shield 2d is secured a metallic cup 25by means of wire 26. Within the cup '25 is a mixture for producing caesium'vapor when heated, the mixture being held in place by a piece of metal gauze 21. The

stem 6 is provided with an exhaust tube 28.

Coil 29 is arranged to induce high frequency current in, the metal cup 25 for heating the mixture within the cup to its reaction tem perature. This coil 29 is used only during the processing of the tube.

Sealed in thepressl are lead-in wires 32, 33

and 34 connected respectively to support wires 8, Hand l2. Consequently, lead-in wire 32 is conductively connected to cathode I 5 and lead-in wires 33 and 34 are conduotively connected respectively to anodes 2i and 22.

A portion of the glass bulb 5 is shown broken away for clearness of illustration.

The cross-sectional shape of the cathode l5 and location of the anode wires 2 l and 22 are more clearly shown inFig. 2 which is a cross-section through the tube at the largest diameter of bulb 5 perpendicular tothe axes of the quarter-cylin ders Hi and I! looking toward the mica disc l3. Due. to the configuration of the cathode l5 and location of the anodes 2| and 22, substantially all of the electronsemitted from eitherportion i6 or I! of the cathode I will be collected by the corresponding anode. In View of this fact the efficiency of this tube when used in the so-calledv push-pull projection circuit is very high.

In order to lengthen the leakage paths along the mica surface between the anodes and cathode, slots 36 are cut in disc l3.

The electrodes and accessory structure carried by the stem 6 are fabricated before the stem is sealed into the glass bulb 5. Cathode I5 is formed from a polished silver sheet of a high degree of purity which has a clean mirror finish. The formed cathode is washed and reduced in hydrogen. The concave surfaces of quarter-cylinders I6 and ll of the cathode l5 have a diameter of approximately 1 inch and the length of the cathode is approximately 1% inchesf The caesium producing mixture within the cup 25 is in the form of a compressed pellet which is composed of approximately 3.5 milligrams of caesium chromate Cs2CrO4, 22.5 milligrams of chromic oxide CI2O3, and 9 milligrams of powdered aluminum Al. These ingredients are carefully prepared, finely pulverized and thoroughly mixed in the proper proportions before being formed into pellets.

The pumping station illustrated in Fig. 3 is adapted for, the processing of four tubes concurrently. The tubes 5 are sealed to a glass header 40 by exhaust tubes 28. This header 40 runs through an oven 4| which comprises a base 42 carrying end supports 43 on the upper ends of which is a metallic cap 44. An electric heater 45 between the supports 43 is surmounted by a removable cover 46 carrying four chimneys 41. This cover is provided with handles 48. The heater 45, cover 46 and chimneys 41 may be raised as a unit so that the chimneys surround the bulbs 5. Each chimney is provided with a slidable bafile (not shown) to control the convection air currents flowing therethrough. With the cover 46 and chimneys 41 removed, the heater 45 may be raised against the cap 44 to completely surround the bulbs 5. I

The header 4!! is connected to a pumping apparatus comprising a liquid air trap 49, two Mc- Leod gauges 50 and 5!, mercury vapor pump 52 and mercury cut-off 53, and a vacuum pump (not shown) connected to tube 54.

Between the mercury cut-off 53 and the liquid air trap 49, two gas supply units 55 and 55 are connected to the pumping apparatus; These units comprise flexible coiled glasstubes 5'! associated with gas containers 58 and 59 through mercury seals surrounding'pairs of porous plugs of Lavite, which plugs when brought together permit gas to pass from the respective containers 58 and 59 to the bulbs 5 through the glass coil 51. An ionization manometer 60 is connected to the other end of the header 40.

An electrical circuit used during the processing of four tubes while they are sealed on a pumping station is illustrated in Fig. 4. This circuit comprises conductors adapted to be connected to a direct current source (not shown) and a potentiometer H for determining the potentials to be applied between cathodes l5 and anodes 2! and 22 in parallel of tubes 5. With switch 12 in its lower position and jack Closed, a potential may be impressed on any one of tubes 5 by closing the lower contacts of switch 13 which is individual to such tube. With switch 12 in its upper position the potential determined by potentiometer H is impressed through the upper contacts of all of. switches 13 in series on condenser 14 which have a total capacitance of 5 microfarads. Condenser 74 can then be discharged through any of tubes 5 by closing the lower contacts of the corresponding switch 13. The voltage determined by potentiometer H is indicated by voltmeter 16. The current flowing through tubes 5 during a later stage of the processing is indicated by an ammeter 18 which may be connected into the circuit by inserting plug Tl into jack 15.

The processing of four tubes after the untreated assemblies have been scaled onto the header 40 will now be described.

The tubes 5 are sealed onto the header 453 with the concave sides of the cathode plates 55 facing directly forward with the bulbs 5 centered with respect to the high frequency coils 29 and at such a height that the cup 25 is approximately mid-way of the coil 29 longitudinally.

The vacuum pump is turned on. Liquid air trap49 is cooled with liquid air. When the pressure has fallen sufliciently the manometer Ell is turned on. The heater 45 without the cover 46 and chimneys 41 is raised to engage the cap 44. Current is turned on to bring the oven temperature up to 400 C. and maintained until the manometer shows a pressure of 5 lO mm. of Hg (millimeters of mercury), or lower, when the current is shut off and the oven allowed to cool. Slow leaks anywhere in the system are indicated if the pressure is not less than 2x 10- mm. of Hg when the tubes are cooled to room temperature. If leaks are indicated they should be eliminated before the processing proceeds. This treatment removes occluded gases from the bulbs but does not cause any chemical reaction in the caesium pellet. The pumping station is then flushed with oxygen from gas supply unit 55 until a clear green haze is obtained in the,

the vacuum pumps and the manometer E6 turned ofi. Additional oxygen is admitted to a pressure of 2.2 mm. of Hg as indicated by McLeod gauge .50. Switch 72 of the electrical circuit of Fig. 4

is set in its lower position and the potentiometer H adjusted so that the voltmeter 16 shows a voltage of 700 volts. Switches 13 are then operated in succession to close theirlower contacts so that. each cathode l5 ,in succession is subjected to positive.ionbombardment. The first effect of such bombardment is to produce a heavy layer of silver oxide on the concave surfaces of cathode I 5, followed by a heating-up of the silver plate and reduction of the layer of silver oxide. The cathodes are allowed to cool, the oxygen pressure again adjusted to 2.2 mm. of Hg and the oxidation, reduction and cooling repeated. The

1 mercury cut-01f 53 is then opened and the oxygen pumped out. This treatment leaves the concave surfaces of each cathode I 5 clean and slightly rough so that it has a uniform matte finish.

After a good vacuum has again been obtained as indicated by manometer 60, the mercury cutoff 53 is again closed and the manometer turned off. A fresh charge of oxygen through gas supply unit 55 is admitted to a pressure of 0.75 mm. of Hg. Switch 12 is thrown to its upper position after potentiometer H has been adjusted so that the voltmeter 16 shows a voltage of' 650 volts. Each tube 5 is then subjected to a series of discharges from condenser 14 by the operation of closing switches 13 on their lower contacts. This operation is hereinafter called tapping.

' Switch 12in its upper position is therefore said the .four tubes. in succession, then the second i group. andsojon. until each; tube has received: the

. required. number of taps or discharges. The

. mercuryP-cut-oif 53 is again opened and the oxygen pumped out. The manometerfill isagain l turned .on and the pumping continued until the :J'Ihis treatment :with oxygen by tapping prois bombarded with a definite number of positive ducesathirr layer of silveroxide on the concave surfacesofeach cathode l5. At eachtappingof awswitch 13 a .glow discharge occursin the associated tube and the cathode 15. of that tube ions. The amount: of silver Foxide which. is

. l The cathodes l5 are now in condition tofbe formed is therefore closely controlled.

treated with caesium lvapor; under suitable temperatureyconditionsh A source of high. frequency,

[current (not. shown) is connected tocoilsis in succession tofflash theucaesium pellets, that is, to induce sufficient current in the cups to start val chemical reaction of theingredients of the caesium pellet. The, exothermic reaction which follows develops a large amount of heat and causes the immediate and complete expulsion of all ofuthe caesium. 'I'hehigh frequency source iswdisconnected as soon as the reaction starts; The caesium, as it travels from the open end of cup 25 throughmetal gauze 2], isdefiected by l, shieldfi24 and is condensed "on the glass walls of the bulb 5 in front of theoxidized surface of a5 thecathode IS. The shield 24 prevents .the hot caesiumyapor from impinging directly on the cathode surface. This shield 24 is so shaped that I it lies substantially parallel to the magnetic lines of force produced by the high frequency current win coil 29 and therefore is not heated to any great extentby eddy-currentsinduced therein.

Immediately after thecaesium pellet has been flashed stem heaters (not shown) are inserted around the stems of the tubes 5. Thermocouples are placed against each bulb 5 at thesurface opposite the stem to indicatetemperatures The cover. 46 with the chimneys 41 are placed on the heater 45 and the whole raised until a chimney 4 surrounds each bulb 5. The stem heaters are turned on first and after two minutes the heater 45.is turned on toquickly bring up the temperature of the convection air currents flowing past the bulbs 5. When the hottest bulblreaches a I temperatureof 150 C. the heater 45 is regulated to hold this temperaturefor five minutes. At the end of this five-minute period the heater 45 is meter'lawhen connected into the circuit ofFig; 4 by the insertion of plug ll into jack .15. Each cathode 15 may be illuminated by a source of light (not shown). The potentiometer H is adjusted to give a voltage of volts, as shown on voltmeter 16. Switch 12 is closed inits lower position. The sensitivity of each tube5 will be indicated by theammeter l8if the corresponding switch 13 is closed; in its lower position. The tubes 5 are tested from time to time while illuminated and thehot air treatment is continued until. the photoelectric current tends to decrease toube inithei-tappingf position, Eachswitch l3; .is tapped sixtywtimeslin three groups oftwenty tapsleachu Thefirst group of tapsis applied to each, tube reaches ,itsproper sensitivity the air.

tubeshave reached the proper. sensitivity the chimneys 41' are lowered and the bulbs allowed to. .cool touroom temperature with the pumping apparatuswstill on.

When the bulbs 5 have cooled and the pressure pressure assumes .asteady state at the desired value, when the tube is sealed off from the header ilthy sealing ofi the exhaust tube 28. The pressure of argon is dependent upon the amount of gastamplification desired in the completed tube.

A suitable pressure is 5x 10- mm. of Hg.

Thecathode it may comprise a nickel or copper sheet having a surface layer of silver which is processed inv the manner hereinbefore described to render it photoemissive. The preliminary roughening of the silver surface may be accomplished in. other Ways than by oxidation and reduction of the silver oxideas, for example, by

sandblasting, etching withacid, or even by applying a coatingof silver oxide and abinder with a brush or air spray and reducing the silver oxide to metallicsilver by heat.

The cathodesmay also be sensitized by subjecting the oxidized silver surface to the vapor of other of the alkali metalsgrubidium, lithium, po-

tassium and sodium. The temperature conditions would be varied somewhat depending upon the materialsbeingused. l

What is claimed is: p

1. A photoelectric tube comprising an evacuated container, a metallic cathode comprising two concave quarter-cylindrical surfaces of quartercircularfcrossesection joined along one edge and curved away from each other so that a straight line joining any point within the quadrant of one surface with any pointiwithin the quadrant of the other surface intersects both surfaces, means supporting said cathodefwithin said container, two anodes also supported within saidcontainer at substantially equal distancesin front of said con: cave cathode surfaces respectively and parallel thereto both anodes lying in a plane which intersects both cathode surfaces-intermediate said 1 anodes, and a light'sensitive electric layer on both said concave surfaces;

2. A photoelectric tube comprising an evacue ated container, a metallic cathode plate having two concave cylindrical continuously curved surfaces joined along one-edge and curved away from each other with no portion of one surface facing any portion of the other surface, means support-h ing said cathodewithin said container, two anodes also supported within said container in front of said concave surfaces respectively and parallel thereto said surfaceslying betweenall portions of the respective anodes, and a light sensitive electric layer on both said concave surfaces.

cylinders, the axes and thejoined edges of which lie substantially in the. same plane, two wire anodes parallel to and in frontof the concave surfaces of said quarter-cylinders respectively closer to said surfaces than the respectiveaxes and between said surfaces and said plane, means supl 4. A photoelectric tube comprising an evacuated container; a continuous metallic cathode plate "formed into two adjacent quarter-circular cylinders, the axes and the joined edges of which lie substantially in the same plane, two wire anodes parallel to and in front of the concave sur- V ated container, a metallic cathode plate having two concave cylindrical continuously curved surfaces joined along one edge and curved away from each other with no portion of one surface facing any port-ioncf the other surface, means supporting said cathode within said container, two anodes also supported within said container in frontoi said concave surfaces respectively and parallel thereto said surfaces lying between all portions of :e respective anodes, and a light sensitive elec-v tron emitting layer on bothsaid concave surfaces comprising an intimatemixture of finely divided silver, caesium oxide and metallic caesium.

6. A photoelectric tube comprising a light pervious envelope with a reentrant stem supporting side by side two parallel continuously-curved sheetlike photoelectric cathodes sensitized with light responsive electron emitting material on one surface, and with adjacent edges joined together and with theperpendicular planes bisecting the light sensitivesurfaces intersecting each other on a line behind the light sensitive surfaces, and electron collecting means in said envelope.

7. A photoelectric tube comprising a light pervious envelope with a reentrant stem supporting side by-side two parallel continuously-curved sheet-like photoelectric cathodes sensitized with light responsive electron emitting material on one surface,- and with adjacent edges joined together and'with the perpendicular planes bisectingthe,

light sensitive surfaces intersecting each other on a line behind the light sensitive surfaces,and two anodes in front of said sensitized surfaces,

tween said anodes; e,

respectively, parallel thereto and lyinglin a plane which intersects both said sensitized surfaces be- 151 8. A photoelectric tube comprising an'evacuated container, a continuous metallic cathode.

plate formed into two adjacent quarter-circular cylinders joined along adjacent edges, the axes and the joined edges of which lie in substantially the same'plane, twowire anodes parallel to and Y in'frcnt of the concave surfaces of said quarter-* cylinders, respectively, each'lying in a plane pass ing'through the parallel edges of the respective concavezsurfaces closer to the outside edge than the joined edge and away from the outside edge by approximately one-third the distance between v the'outside edge and the joined edges, means supporting said cathode and anodes within said container, and a light sensitive electric layer on said concave surfaces. I

'- WALTER J. ALBERSHEIML 

